VoIP call control apparatus in private branch exchange and method thereof

ABSTRACT

A VoIP call control apparatus in a PBX (Private Branch exchange) and a method thereof is capable of an effective charge management by differentiating bandwidth allocation according to a service level. The VoIP call control apparatus in a PBX includes: a service class decision unit for receiving a VoIP call service request from a subscriber, deciding a service class, and outputting the service class; a service level decision unit for measuring a service level of a VoIP trunk and outputting the service level; a C/O matching unit for matching a PSTN network and the PBX; a VoIP gateway for performing a protocol matching process with respect to an outgoing call from the PBX, and providing a voice call conforming to VoIP protocol; a G/W matching unit for matching the VoIP gateway and the PBX; and a signal processing unit for deciding whether the VoIP call with the service class transmitted from the service decision unit can be serviced in the service level of the VoIP trunk transmitted from the service level decision unit, and if the VoIP call is serviceable, providing a VoIP call service through the G/W matching unit and the VoIP gateway, and if the VoIP call is not serviceable, providing a voice call service over the PSTN network via the C/O matching unit.

CLAIM OF PRIORITY

[0001] This application makes reference to, incorporates the sameherein, and claims all benefits accruing under 35 U.S.C. §119 from anapplication for “Call Control Apparatus in Private Branch exchange andMethod Thereof” earlier filed in the Korean Intellectual Property Officeon 13 Dec. 2002 and there duly assigned Serial No. 2002-79836.

BACKGROUND OF THE INVENTION

[0002] 1. Field of the Invention

[0003] The present invention generally relates to a VoIP (Voice overInternet Protocol) call control apparatus in a PBX (Private Branchexchange) and a method thereof, and more particularly, to a VoIP callcontrol apparatus in a PBX, capable of an effective charge management bydifferentiating bandwidth allocation according to a service level, and amethod thereof.

[0004] 2. Description of Related Art

[0005] In general, a PBX or a keyphone system refers to a telephoneexchange facility (e.g. interphone-to-telephone connection ortelephone-to-interphone connection) established in government and publicoffices, corporations, or hospitals.

[0006] In the PBX, an extension telephone is accessed to a SLIC(Subscriber Line Interface Card) accommodating local subscribers, and atrunk card is accessed to a CO Line (Central Office Line) connected to apublic exchange. Thus, a plurality of local subscribers can exchangecalls with each other without going through an external central officeline, and when they want to call outside, they simply need to press atrunk access code (usually, No. ‘9’) and dial a telephone number theyintended to call.

[0007] Generally, a subscriber's extension line accessed to the PBX iscomposed of an extension line for covering general analog telephones, akeyphone line for covering keyphone telephones, an ISDN BRI (ISDN BasicRate Interface) for covering ISDN (Integrated Services Digital Network)11 telephones, and so forth. These lines are connected to a backboard ofa matching device mounted in each PBX.

[0008] Central office line accessed to the PBX includes analog trunk(general CO line), digital trunk including E1 line (a high speedcommunication line according to a European specification and one of theE-carrier systems) or T1 (a high speed communication line and one of theT-carrier systems), ISDN PRI (ISDN Primary Rate Interface) line and thelike. Again, these lines are connected to the backboard of the matchingdevice mounted in the PBX.

[0009] Originally, VoIP referred to an IP telephone technique for setsof equipments for transferring voice information using an IP (InternetProtocol). Currently, VoIP indicates digitalized voice informationtransfer to discontinuous packets in a digital system, unliketraditional protocols based on a circuit such as PSTN (Public SwitchedTelephone Network).

[0010] The best advantage of VoIP and Internet telephone technique isintegrated implementation of telephone services utilizing an existing IPnetwork. In other words, telephone users are provided with long-distanceand international telephone services in Internet, and Intranetenvironments at the Internet access charge only.

[0011] In case of having voice calls through the VoIP, because thepublic network cannot provide the quality of service (QoS) equivalent toone in a circuit network, a private network managed by a specialbusiness or Internet phone service operator (hereinafter, referred to as‘special category telecommunications operator’) is preferred to gethigh-quality services.

[0012] In such case, the special category telecommunications operatorhas a server for managing IP addresses according to telephone numbers ofthe other parties. Hence, the user does not need to manage an IP addressfor the other party's telephone number every time he/she makes a voicecall over the Internet.

[0013] To use VoIP in the PBX, a gateway is required. The gateway is incharge of receiving voice data packets from users and transferring themto destinations over networks, including Internet and Intranet, anddirectly connecting a corresponding call to PSTN using an analog trunk,or T1 or E1 interface.

[0014] Typically, in the case of accessing VoIP gateway to the PBX, thecentral office line accessed to the Vo/P gateway from the PBX isisolated and different access codes are given.

[0015] For instance, if an extension subscriber wants to make anoutbound voice call through the VoIP gateway, ‘8’ can be assigned as thetrunk access code, and if an extension subscriber wants to make anoutbound call through a general CO line connected to the PSTN, ‘9’ canbe assigned as the trunk access code, thereby distinguishing thesecodes.

[0016] In addition, if an extension subscriber wants to make a voicecall through the VoIP gateway, only outgoing calls are possible in thecommunication with the other party using the VoIP, and incoming callsare available for the CO line.

[0017] To make a VoIP call, a user first needs to check the dial tonefrom the PBX, and dials a number for connection to the VoIP gatewaybetween TCP (Transmission Control Protocol) and IP (Internet Protocol)network (Internet).

[0018] At this time, the VoIP gateway looks up a routing table to findout if the input number is a serviceable number.

[0019] If not, the VoIP gateway checks whether it is necessary toconnect the call through another VoIP gateway. If this is not the case,the VoIP gateway returns corresponding information back to the PBX, toencourage making the call through a general telephone network.

[0020] If the VoIP gateway finds an Internet route corresponding to theinput number, the call is connected. To do so, the gateway should securea circuit between itself and the VoIP gateway of the other party.

[0021] After that, the VoIP gateway of the caller modulates the voice ofthe caller to an IP packet, as if it were transferring a correspondingdata packet, and sends the corresponding IP packet to a given route overthe TCP/IP network.

[0022] Meanwhile, receiving the IP packet data, the VoIP gateway on thereceiving side recovers an analog signal by recombining packetinformation, and routes the restored signal to a call through the PSTNin the exchange office or through another PBX, and connects the calldirectly to a receiving telephone. In this manner, the voice callrouting procedure over Internet is completed.

[0023] Taking advantage of VoIP techniques, network operators are ableto route telephone calls over the network, just like using for data, andbased on this, provide users with VoIP call services at a low price.

[0024] In many cases, a VoIP network is established between theheadquarters of a company and branches, to reduce phone charges. TheVoIP services available over this VoIP are as follows:

[0025] Long-distance calls between the headquarters and branches usingIP network;

[0026] Long-distance calls between the headquarters and branches usingPSTN network; and

[0027] International calls between the headquarters and branchsubscribers through an international gateway office of internationaltelephone network connected to PSTN (cf. the connection between theheadquarters and branches is established through IP network).

[0028] At this time, if a subscriber accessed to each PBX tries to makea long-distance call or an international call, IP-PBX allocates a VoIPport and provides VoIP services in sequence, as long as a serviceableVoIP trunk exists.

[0029] However, there are not as many VoIP trunk ports as subscribers.Therefore, allocating one VoIP trunk port to five subscribers(Subscriber: VoIP trunk port=5:1), all subscribers can use the VoIPtrunk port. Nevertheless, as VoIP calls increase, more VoIP trunk portswill have to be allocated and then it will be all in a busy state.

[0030] In such case, the subscribers cannot use VoIP calls because thereis no available VoIP trunk for them, but use a relatively expensive PSTNtrunk.

[0031] Moreover, if long-distance VoIP calls, which are notcost-effective compared to international VoIP calls, are involved,international call services are not going to be provided for a followingVoIP call. As a result, from the perspective of cost-reduction throughVoIP trunks of IP-PBX, it seems like a plurality of “inexpensive calls”occupies “inexpensive lines” and “expensive calls” cannot use“inexpensive lines” after all.

SUMMARY OF THE INVENTION

[0032] An object of the invention is to solve at least the aboveproblems and/or disadvantages and to provide at least the advantagesdescribed hereinafter.

[0033] Accordingly, one object of the present invention is to solve theforegoing problems by providing a method for controlling VoIP calls inPBX, to take advantage of a VoIP trunk that is relatively cost-effectivein the PBX having subscribers, PSTN trunks and VoIP trunks.

[0034] Another object of the present invention is to provide a methodfor controlling VoIP calls in PBX, wherein VoIP service levels aredefined according to the state of a VoIP call service, andcost-effective VoIP call services are controlled, depending on class ofservice per VoIP service level.

[0035] Still another object of the present invention is to provide amethod for controlling VoIP calls in PBX, wherein cost-effective VoIPservices are controlled in accordance with kind of call (e.g.international call, long-distance call, headquarters-to-branch call) perVoIP service level.

[0036] The foregoing and other objects and advantages are realized byproviding a VoIP call control apparatus in a PBX (Private BrancheXchange), the apparatus including: a service class decision unit forreceiving a VoIP call service request from a subscriber, deciding aservice class, and outputting the service class; a service leveldecision unit for measuring a service level of a VoIP trunk andoutputting the service level; a C/O (central office) matching unit formatching a PSTN network and the PBX; a VoIP gateway for performing aprotocol matching process with respect to an outgoing call from the PBX,and providing a voice call conforming to VoIP protocol; a G/W (gateway)matching unit for matching the VoIP gateway and the PBX; and a signalprocessing unit for deciding whether the VoIP call with the serviceclass transmitted from the service decision unit can be serviced orestablished in a service level of the VoIP trunk decided in the servicelevel transmitted from the service level decision unit, and if the VoIPcall is serviceable, providing a VoIP call service through the G/Wmatching unit and the VoIP gateway, and if the VoIP call is notserviceable, providing a voice call service over the PSTN network viathe CIO matching unit.

[0037] Another aspect of the invention provides a VoIP call controlmethod in a PBX (Private Branch exchange), the method including thesteps of: in the PBX, if a subscriber sends a VoIP call service request,deciding a VoIP service class; deciding whether the VoIP call servicecan be provided in a VoIP trunk service level corresponding to the VoIPservice class; if the VoIP call service cannot be provided, providing avoice call service through a PSTN network, and if the VoIP call servicecan be provided, looking up an available VoIP trunk port and providingthe VoIP call service through the VoIP trunk; and when providing theVoIP call service, changing the VoIP trunk service level.

BRIEF DESCRIPTION OF THE DRAWINGS

[0038] A more complete appreciation of the invention, and many of theattendant advantages thereof, will be readily apparent as the samebecomes better understood by reference to the following detaileddescription when considered in conjunction with the accompanyingdrawings in which like reference symbols indicate the same or similarcomponents, wherein:

[0039]FIG. 1 is a diagram illustrating a VoIP network architecture towhich the present invention is applied;

[0040]FIG. 2 is a schematic diagram of a VoIP call control apparatus ina PBX according to an exemplary embodiment of the present invention; and

[0041]FIG. 3 is a flow chart describing a method for controlling VoIPcalls in a PBX according to an exemplary embodiment of the presentinvention.

DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS

[0042] Reference will now be made in detail to exemplary embodiments ofthe present invention, which are illustrated in the accompanyingdrawings.

[0043]FIG. 1 is a diagram illustrating a VoIP network architecture towhich the present invention is applied.

[0044] Referring to FIG. 1, the PBX 110 in the headquarters has a VoIPtrunk, and is connected to an IP network and a PSTN network. Also, thePBX 110 is connected to an international gateway office 140 via the PSTNnetwork.

[0045] In like manner, each of branch PBXs 120 and 130 has a VoIP trunk,respectively, and is connected to the IP network and the outbound PSTNnetwork.

[0046] Thus, telephone communications between the headquarters andbranches over IP network are possible through PBXs 110, 120 and 130mounted with VoIP trunks. Telephone communications between branches arealso possible using the PBXs 120 and 130 with VoIP trunks.

[0047] At this time, the headquarters and each of the branches areassigned with a necessary bandwidth, for example, 512 kbps (kilobits persecond) to the headquarters and 256 kbps to each branch.

[0048] Moreover, each of the PBXs 110, 120 and 130 is interconnectedwith the PSTN network, and thus, PSTN network based-telephonecommunications between a branch and another branch, and between theheadquarters and a branch are possible.

[0049] Because the PBX 110 of the headquarters is connected to theinternational gateway office 140 via the PSTN network, each of thebranches can make international calls through the international gatewayoffice 140 via its own PBX 120 or 130 and the PBX 110 of theheadquarters.

[0050] Of course, long-distance call services are also available throughthe PBX 110 of the headquarters and the PBXs 120 and 130 of thebranches.

[0051] Each of the PBXs 110, 120 and 130 defines a class of serviceassociated with a VoIP call per subscriber. For example, the class ofservice for subscribers who make international and long-distance callsfrequently is ‘0’ (e.g. Export Dept.), and the class of service forsubscribers who make long-distance calls frequently is ‘1’ (e.g.Domestic Marketing Dept.).

[0052] In addition, the class of service for subscribers who makelong-distance calls between the headquarters and a branch for most ofthe time is ‘2’ (e.g. Manufacture Management Dept.). Lastly, the classof service for other subscribers is ‘3’.

[0053] Next, a network bandwidth is assigned to each of the PBXs 110,120 and 130 (refer to Table 1) (for instance, Silence Enable to G723.1Codec (coder/decoder), and 8.3 kbps to the Multiframe 1 environment).Every time a VoIP call service is provided, the bandwidth is increasedproportionally, and the VoIP trunk service level (refer to Table 2) ismeasured based on a total bandwidth being available (e.g. 512 kbps forthe headquarters). TABLE 1 G.723.1 6.3K G.729A Codec Silence SilenceSilence Silence Frame Enable Disable Enable Disable 1 8.3K 20.8K 20.5K51.2K 2 5.4K 13.6K 11.8K 29.6K 3 4.9K 11.2K  9.0K 22.4K 4 4.4K 10.9K 7.5K 18.8K 5 3.7K  9.3K  6.6K 16.6K 6 3.5K  8.8K  6.1K 15.2K 7  5.6K14.1K 8  5.4K 13.4K 9  5.1K 12.8K 10   4.9K 12.3K

[0054] TABLE 2 VoIP Trunk Service Level Standard (VoIP bandwidth usage:%) 3 Below 50% 2 Greater than or equal to 50% and Below 70% 1 Greaterthan or equal to 70% and Below 80% 0 Greater than or equal to 80% andBelow 90%

[0055] As shown in Table 2, when the VoIP bandwidth usage is below 50%,the VoIP trunk service level is 3, far from being busy, to be morespecific, in a light traffic state where the VoIP call service is yetavailable.

[0056] In this case, the class of VoIP service per subscriber discussedabove or the class of VoIP service according to the type of call that isgoing to be discussed later does not need to be considered. As such,selective call setup is not required, and all VoIP calls being requiredcan be covered.

[0057] If the VoIP bandwidth usage is greater than or equal to 50%, butbelow 70%, the VoIP trunk service level is 2, a little closer to a busystate.

[0058] In this case, the class of VoIP service per subscriber discussedabove or the class of VoIP service according to the type of call that isgoing to be discussed later should be considered. As the traffic isbeing increased, selective call connection is required.

[0059] With respect to the class of service, only one or both VoIPservice class per subscriber and VoIP service class according to thetype of call can be considered at the same time.

[0060] If the VoIP bandwidth usage is greater than or equal to 70%, butbelow 80%, the VoIP trunk service level is 1, a busy state.

[0061] In this case, to reduce phone rates, only VoIP calls of highranks in the class of VoIP service per subscriber discussed above or inthe class of VoIP service according to the type of call that is going tobe discussed later are covered.

[0062] With respect to the class of service, only one or both VoIPservice class per subscriber and VoIP service class according to thetype of call can be considered at the same time.

[0063] If the VoIP bandwidth usage is greater than or equal to 80%, butbelow 90%, the VoIP trunk service level is 0, a very busy state or heavytraffic state. In this state, a great deal of VoIP call services isbeing already provided.

[0064] To reduce phone rates in the heavy traffic state, only VoIP callsof the highest rank in the class of VoIP service per subscriberdiscussed above or in the class of VoIP service according to the type ofcall that is going to be discussed later are covered.

[0065] Another option to reduce phone rates in the heavy traffic stateis to cover only VoIP calls that satisfy requirements of both VoIPservice class per subscriber and VoIP service class according to thetype of call.

[0066] Each of the PBXs 110, 120 and 130 methodizes VoIP calls in theorder of cost-reduction effect, namely international calls>long-distancecalls>headquarters-to-branch calls, and distinguishes the class ofservice according to the type of call. Table 3 illustrates availableVoIP trunk service levels in each class according to the type of call.TABLE 3 Available VoIP VoIP Call Type Trunk Service Levels 0(International calls) 0, 1, 2, 3 1 (Long-distance calls) 1, 2, 3 2(Headquarter-to-Branch calls) 2, 3

[0067] As shown in Table 3, available VoIP trunk service levels forinternational calls are 0, 1, 2 and 3. If there is a margin of the VoIPtrunk, a VoIP bandwidth can be assigned at any time to connect calls.

[0068] Next, available VoIP trunk service levels for long-distance callsare 1, 2 and 3. Provided that the VoIP trunk service level having theVoIP bandwidth usage below 90% is 0, subscribers can make calls onlythrough the PSTN network.

[0069] Lastly, available VoIP trunk service levels forheadquarters-to-branch calls are 2 and 3. Provided that the VoIP trunkservice level having the VoIP bandwidth usage below 90% is 0, and thatthe VoIP trunk service level having the VoIP bandwidth usage below 80%is 1, subscribers can make calls only through the PSTN network.

[0070] At any rate, VoIP calls are increased proportionally tointernational and long-distance calls originated by the subscribers. Assuch, the VoIP traffic as well as the VoIP service level is changed.

[0071] If that happens, it is not going to be easy for the subscribersto use the VoIP service any more, and they will have to compete againsteach other for limited VoIP trunk ports.

[0072] Unfortunately, to maximize cost-reduction having limited VoIPtrunk ports according to VoIP service environments, the existingsequential servicing method is not the best option to meet the VoIP callservice request.

[0073] Therefore, it is necessary to measure VoIP service based on anoccupancy rate of bandwidth per VoIP call, and classify the class ofsubscriber or available service level per call type, and assign a VoIPtrunk according to the VoIP service level being measured.

[0074] Table 4 is the list of available VoIP trunk service levelsaccording to different class of VoIP service per subscriber. TABLE 4Subscriber VoIP Available VoIP Trunk Service Class Service Levels 0 0,1, 2, 3 1 1, 2, 3 2 2, 3 3 3

[0075] Each of the PBXs 110, 120 and 130 defines the class of VoIP callservice per subscriber. For instance, the class of service forsubscribers who make international and long-distance calls frequently is‘0’ (e.g. Export Dept.), and the class of service for subscribers whomake long-distance calls frequently is ‘1’ (e.g. Domestic MarketingDept.).

[0076] In addition, the class of service for subscribers who makelong-distance calls between the headquarters and a branch for most oftime is ‘2’ (e.g. Manufacture Management Dept.). Lastly, the class ofservice for other subscribers is ‘3’.

[0077] If the class of VoIP service of a subscriber is 0, this means thesubscriber, probably in Export Dept., makes a lot of internationalcalls. Because PSTN-based calls are expensive in this case, thesubscriber can reduce phone rates by calling over the VoIP network.

[0078] Next, if the class of VoIP service of a subscriber is 1, thismeans the subscriber, probably in Domestic Marketing Department, makes alot of long-distance calls. Compared to international calls,long-distance calls are inexpensive. Hence, available service levels forthe Domestic Market Department are limited, compared to the ones for theExport Department. The subscriber can make VoIP calls when the VoIPtrunk service level is 1, 2 or 3.

[0079] If the class of VoIP service of a subscriber is 2, this means thesubscriber, probably in Manufacture Management Department, makes a lotof long-distance calls between the headquarters and branches. Hence,available service levels for the Manufacture Management Department areeven more limited than the ones for the Export Department. Thesubscriber can make VoIP calls when the VoIP trunk service level is 2 or3.

[0080] Lastly, if the class of VoIP service of a subscriber is 3, thismeans the subscriber is probably involved in other kinds of work. Theservice area is very limited in this case, and the subscriber can makeVoIP calls only when the VoIP trunk service level is 3.

[0081] Although the VoIP trunk service level is divided into 4 kinds,i.e. 0, 1, 2 and 3, it can be specified further.

[0082] Similarly, although the class of VoIP service per subscriber iscategorized by department, other kinds of categories can also be used.Moreover, the class of service can be specified further.

[0083] In particular, the class of VoIP service for international callscan be graded according to country. The class of VoIP service forlong-distance calls can also be specified further.

[0084] VoIP calls can be limited or permitted, on the basis of not onlythe class of VoIP service per subscriber, but also the class of VoIPservice per call type. After all, these two standards are used forlimiting or permitting calls.

[0085] VoIP trunk service level can be graded in terms of enhancing workefficiency of a company and other factors. If there is any one who wantsa better voice quality, he/she may be allowed to set a call over thePSTN.

[0086] In short, the PBX can divide service level and class of servicebased on more diverse categories, in consideration of cost-reduction andmore effective business activities.

[0087]FIG. 2 is a schematic diagram of a VoIP call control apparatus ina PBX according to an exemplary embodiment of the present invention.

[0088] Referring to FIG. 2, the VoIP call control apparatus in a PBXincludes a service class decision unit 210, a signal processing unit220, a C/O matching unit 230, a G/W matching unit 240, a VoIP gateway250, and a service level decision unit 260.

[0089] If a subscriber requests a call connection, the service classdecision unit 210 looks up the class of service of a subscriber listedin the pre-stored subscriber service class table, and outputs the classof service to the signal processing unit 220.

[0090] The service class decision unit 210 decides the class of service,conforming to the pre-stored service class table per call type, andoutputs the class of service to the signal processing unit 220.

[0091] In addition, when the subscriber requests a call connection, theservice class decision unit 210 looks up the subscriber service classtable to find out the class of service of the subscriber, and outputsthe result to the signal processing unit 220. Also, the service classunit 210 decides class of the service by looking up the service classtable per call type, and outputs the result to the signal processingunit 220.

[0092] The signal processing unit 220 stores the VoIP service classtable per call type (Table 3) or the VoIP service class table persubscriber (Table 4). Referring to the VoIP service class tables, theservice level of the current VoIP trunk from the service level decisionunit 260 and the class of service from the service class decision unit210 are searched. Then the signal processing unit 220 transfers a callto the PSTN network through the C/O matching unit 230, or to the VoIPgateway and eventually the IP network through the C/O matching unit 230,conforming to the search result.

[0093] The signal processing unit 220 can decide where to transmit thecall, in consideration of one or both of the VoIP service class tableper call type and the VoIP service class table per subscriber.

[0094] The C/O matching unit 230 is connected to both PBX and PSTNnetwork, matching these two. Similarly, the G/W matching unit 240 isconnected to both PBX and VoIP gateway 250, matching these two.

[0095] The VoIP gateway 250 connected to the G/W matching unit 240 is adevice for protocol matching with respect to an outgoing call from thePBX. It is connected to a call receiver over the Internet, and providesthe call receiver with a voice call according to the VoIP protocol.

[0096] The service level decision unit 260 accumulates bandwidthproportionally to VoIP calls being serviced, and decides the servicelevel of VoIP trunk based on the occupancy rate of the accumulatedbandwidth out of the total bandwidth. Then the service level decisionunit 260 outputs the service level of VoIP trunk to the signalprocessing unit 220.

[0097] More details on the operation of the VoIP call control apparatusin the PBX are provided below.

[0098] Each PBX assigns a network bandwidth as shown in Table 1. Forexample, Silence Enable is assigned to G723.1 codec, and 8.3 kbps isassigned to the Multiframe 1 environment. Every time a VoIP call isconnected, the service level decision unit 260 accumulates bandwidthproportionally to VoIP calls being serviced, and measures the servicelevel of VoIP trunk based on the occupancy rate of the accumulatedbandwidth out of total bandwidth being available (e.g. 512 kbps for theheadquarters), as shown in Table 2. Then the service level decision unit260 outputs the service level of VoIP trunk being measured to the signalprocessing unit 220.

[0099] For instance, suppose that the total bandwidth available for theheadquarters is 512 kbps. If the currently accumulated bandwidth is 332kbps, the occupancy rate is 64%. As such, the service level decisionunit 260 concludes that the service level of the VoIP trunk is ‘2’, andtransfers this level ‘2’ to the signal processing unit 220.

[0100] The service class decision unit 210 has the service class tableper subscriber or the service class table per call type. Hence, whenthere is a call connection request, the service class decision unit 210looks up each of the service class tables to find out an appropriateservice class with respect to the call connection request, and transfersthe service class to the signal processing unit 220.

[0101] For instance, if a subscriber in the Manufacture ManagementDepartment sends a call connection request, the service class decisionunit 210 looks up the VoIP service class table per subscriber, and givesthe subscriber the class ‘2’. Then, the service class decision unit 210transfers the class to the signal processing unit 220. In like manner,if a subscriber in the headquarters sends a call connection request, theservice class decision unit 210 looks up the VoIP service class tableper call type, and gives the subscriber the class ‘2’. Then, the serviceclass decision unit 210 transfers the class to the signal processingunit 220.

[0102] As discussed before, the service class decision unit 210 can makea decision on the service class, referring to both of the VoIP serviceclass table per subscriber and the VoIP service class table per calltype. Suppose that a subscriber in Export Department sends a callconnection request. Then, the service class decision unit 210 outputsthe VoIP service class of the subscriber as ‘0’ based on what is in theVoIP service class table per subscriber. On the other hand, if thesubscriber wants to call to another branch, the service class decisionunit 210 outputs the VoIP service class of the call type as ‘2’ based onwhat is in the VoIP service class table per call type. The service classresult is transferred to the signal processing unit 220.

[0103] Now referring to one of the VoIP service class table persubscriber (Table 3) and the VoIP service class table per call type(Table 4), the signal processing unit 220 decides whether the serviceclass provided by the service class decision unit 210 is qualified for aVoIP service in the VoIP trunk service level provided by the servicelevel decision unit 250.

[0104] If yes, the signal processing unit 220 transfers the call to theG/W matching unit 240, but if not, the signal processing unit 220transfers the call to the PSTN network via the C/O matching unit 210.

[0105] As an example, suppose that the service level transmitted fromthe service level decision unit 260 is 2 and that the VoIP service classof the subscriber transmitted from the service class decision unit 210is 2. Since a VoIP service can be provided in this case, the signalprocessing unit 220 transfers a call through the G/W matching unit 240.Meanwhile, if the VoIP service class of the subscriber is 3 while theservice level is being 2, a VoIP service cannot be provided. Thus thesignal processing unit 220 transfers the call to the PSTN network viathe C/O matching unit 230.

[0106] As another example, suppose that the service level transmittedfrom the service level decision unit 260 is 1 and that the VoIP serviceclass of the call in question transmitted from the service classdecision unit 210 is also 1. Since a VoIP service can be provided inthis case, the signal processing unit 220 transfers the call through theG/W matching unit 240. Meanwhile, if the VoIP service class of thesubscriber is 2 while the service level is being 1, a VoIP servicecannot be provided. Thus the signal processing unit 220 transfers thecall to the PSTN network via the C/O matching unit 230.

[0107] Next, suppose that the service level transmitted from the servicelevel decision unit 260 is 1, the VoIP service class of the subscribertransmitted from the service class decision unit 210 is 1, and the VoIPservice class of the call in question is 1. Since a VoIP service can beprovided according to the VoIP service class of the subscriber, and thecall connection is also possible according to the VoIP service of thecall in this case, the signal processing unit 220 transfers the callthrough the G/W matching unit 240.

[0108] Also suppose that the service level transmitted from the servicelevel decision unit 260 is 1, the VoIP service class of the subscribertransmitted from the service class decision unit 210 is 1, and the VoIPservice class of the call in question is 2. In this case, a VoIP servicecan be provided as long as the VoIP service class of the subscriber is 1while the service level is being 1. However, the VoIP service cannot beprovided if the VoIP service class of the call is 2 while the servicelevel is being 1. Thus the signal processing unit 220 transfers the callto the PSTN network via the C/O matching unit 230.

[0109] The VoIP gateway 250 converts the call transmitted through theG/W matching unit 240 into an appropriate signal for the VoIP protocol,and transfers the converted signal to the IP network.

[0110]FIG. 3 is a flow chart describing a method for controlling VoIPcalls in a PBX according to an exemplary embodiment of the presentinvention.

[0111] Referring to FIG. 3, the method for controlling a VoIP call in aPBX is largely divided into three parts: one is to decide the serviceclass (S110, 112, and 116), another is to decide whether a VoIP servicecan be provided in a service level in question (S114 and 118), and theother is to provide the VoIP service (S120, 122, 124, and 126).

[0112] At first, when the PBX receives a VoIP call service request froma subscriber (S110), it decides the VoIP service class by referring tothe VoIP service class table per subscriber (S112).

[0113] Next, it is decided whether a VoIP service can be provided in aVoIP trunk service level corresponding to the VoIP service class of thesubscriber (S114).

[0114] If the VoIP service can be provided in a VoIP trunk service levelcorresponding to the VoIP service class of the subscriber, a VoIPservice class for the call in question is decided, referring to the VoIPservice class table per call type (S116).

[0115] If the VoIP service cannot be provided in a VoIP trunk servicelevel corresponding to the VoIP service class of the subscriber,however, a voice call service is provided through the PSTN networkinstead (S126).

[0116] On the other hand, it is decided whether a VoIP call service canbe provided in a VoIP trunk service level corresponding to the VoIPservice class of the call (S118). If yes, an available VoIP trunk portis looked up (S120), and the VoIP call service is provided through theavailable VoIP trunk port (S122). On the contrary, if the VoIP servicecannot be provided in a VoIP trunk service level corresponding to theVoIP service class of the call, a voice call service is provided throughthe PSTN network instead (S126).

[0117] Afterwards, a network bandwidth assigned to provide a VoIP callservice is accumulated, and the service level of a VoIP trunk ismeasured according to the occupancy rate of the accumulated bandwidthout of the total bandwidth (S124).

[0118] In conclusion, according to the present invention, a relativelymore cost-effective VoIP trunk can be advantageously used in a PBXhaving PSTN trunk and VoIP trunk.

[0119] In addition, it is possible to control cost-effective VoIP callservice by selectively providing the service according to the class ofservice of the subscriber.

[0120] Further, it is possible to control cost-effective VoIP callservice by selectively providing the service according to the type ofcall (e.g. international call, long-distance call, orheadquarters-to-branch call).

[0121] While the present invention has been particularly shown anddescribed with reference to exemplary embodiments thereof, it will beunderstood by those skilled in the art that the foregoing and otherchanges in form and details may be made therein without departing fromthe spirit and scope of the present invention.

What is claimed is:
 1. A voice over Internet protocol call controlapparatus in a voice over Internet protocol private branch exchange, theapparatus comprising: a service class decision unit for receiving avoice over Internet protocol call service request from a subscriber,deciding a service class for indicating priority of a voice overInternet protocol call service, and outputting the service class; aservice level decision unit for measuring band width usage of the voiceover Internet protocol trunk, deciding a service level according to theband width usage so as to determine which service classes can use thevoice over Internet protocol call service, and outputting the servicelevel; and a signal processing unit for deciding whether the voice overInternet protocol call with the service class transmitted from theservice class decision unit can be serviced in the service level of thevoice over Internet protocol trunk transmitted from the service leveldecision unit, and when the voice over Internet protocol call isserviceable, providing a voice over Internet protocol call service andwhen the voice over Internet protocol call is not serviceable, providinga voice call service over the public switched telephone network.
 2. Theapparatus according to claim 1, wherein the service level decision unitaccumulates a bandwidth every time a voice over Internet protocol callservice is provided, and decides the service level of the voice overInternet protocol trunk according to an occupancy rate of theaccumulated bandwidth out of total bandwidth.
 3. The apparatus accordingto claim 1, wherein the service class decision unit decides the class ofservice by referring to a voice over Internet protocol service classtable per subscriber according to a characteristic of the subscriber. 4.The apparatus according to claim 3, wherein the voice over Internetprotocol service class table per subscriber reflects characteristics ofeach department in a company.
 5. The apparatus according to claim 1,wherein the service class decision unit decides the class of service byreferring to a voice over Internet protocol service class table per calltype according to a type of the call.
 6. The apparatus according toclaim 5, wherein the voice over Internet protocol service class tableper call type reflects characteristics of each call.
 7. The apparatusaccording to claim 1, wherein the service class decision unit decidesthe class of service by referring to both a voice over Internet protocolservice class table per subscriber according to a characteristic of thesubscriber and a voice over Internet protocol service class table percall type according to a characteristic of the call requested.
 8. Theapparatus according to claim 7, wherein the voice over Internet protocolservice class table per subscriber is prepared based on characteristicsof each department in a company, and the voice over Internet protocolservice class table per call type is prepared based on characteristicsof each call.
 9. The apparatus according to claim 1, wherein the serviceclass decision unit decides the class of service by referring to costfor a voice over Internet protocol service of the call.
 10. Theapparatus according to claim 1, further comprising: a central officematching unit for matching a public switched telephone network and theprivate branch exchange; a voice over Internet protocol gateway forperforming a protocol matching process with respect to an outgoing callfrom the private branch exchange, and providing a voice call conformingto voice over Internet protocol; and a gateway matching unit formatching the voice over Internet protocol gateway and the private branchexchange.
 11. A voice over Internet protocol call control method in aprivate branch exchange, the method comprising the steps of: in theprivate branch exchange, when a subscriber sends a voice over Internetprotocol call service request, deciding a voice over Internet protocolservice class; deciding whether the voice over Internet protocol callservice can be provided in a voice over Internet protocol trunk servicelevel corresponding to the voice over Internet protocol service class;when the voice over Internet protocol call service cannot be provided,providing a voice call service through a public switched telephonenetwork, and when the voice over Internet protocol call service can beprovided, looking up an available voice over Internet protocol trunkport and providing the voice over Internet protocol call service throughthe voice over Internet protocol trunk; and when providing the voiceover Internet protocol call service, changing the voice over Internetprotocol trunk service level.
 12. The method according to claim 11,wherein the private branch exchange decides the service class byreferring to a voice over Internet protocol service class table persubscriber according to a characteristics of the subscriber.
 13. Themethod according to claim 11, wherein the private branch exchangedecides the service class by referring to a voice over Internet protocolservice class table per call type according to a characteristic of thecall.
 14. The method according to claim 11, wherein the private branchexchange decides the service class by referring to both a voice overInternet protocol service class table per subscriber according to acharacteristics of the subscriber and a voice over Internet protocolservice class table per call type according to a characteristic of thecall.
 15. The method according to claim 11, wherein the voice overInternet protocol trunk service level is decided based on an occupancyrate of a bandwidth out of a total bandwidth, the bandwidth beingaccumulated every time a voice over Internet protocol call service isprovided.
 16. An apparatus comprising: a first unit receiving a voiceover Internet protocol call service request from a subscriber, decidinga service class, and outputting the service class; a second unitmeasuring a service level of a voice over Internet protocol trunk andoutputting the service level; a third unit matching a public switchedtelephone network and a private branch exchange; a fourth unitperforming a protocol matching process with respect to an outgoing callfrom the private branch exchange, and providing a voice call conformingto voice over Internet protocol; a fifth unit matching the fourth unitand the private branch exchange; and a sixth unit deciding whether thevoice over Internet protocol call with the service class transmittedfrom the first unit can be serviced or established in a service level ofthe voice over Internet protocol trunk decided in the service leveltransmitted from the second unit, and when the voice over Internetprotocol call is serviceable, providing a voice over Internet protocolcall service through the fifth unit and the fourth unit, and when thevoice over Internet protocol call is not serviceable, providing a voicecall service over the public switched telephone network via the thirdunit.
 17. The apparatus according to claim 16, wherein the second unitaccumulates a bandwidth every time a voice over Internet protocol callservice is provided, and decides the service level of the voice overInternet protocol trunk according to an occupancy rate of theaccumulated bandwidth out of a total bandwidth.
 18. The apparatusaccording to claim 16, wherein the first unit decides the class ofservice by referring to a voice over Internet protocol service classtable per subscriber according to a characteristic of the subscriber.19. The apparatus according to claim 18, wherein the voice over Internetprotocol service class table per subscriber reflects characteristics ofeach group of subscribers from a plurality of groups of subscribers. 20.The apparatus according to claim 16, wherein the first unit decides theclass of service by referring to a voice over Internet protocol serviceclass table per call type according to a type of the call.
 21. Theapparatus according to claim 20, wherein the voice over Internetprotocol service class table per call type reflects characteristics ofeach call.
 22. The apparatus according to claim 16, wherein the firstunit decides the class of service by referring to both a voice overInternet protocol service class table per subscriber according to acharacteristic of the subscriber and a voice over Internet protocolservice class table per call type according to a characteristic of thecall requested.
 23. The apparatus according to claim 22, wherein thevoice over Internet protocol service class table per subscriber isprepared based on characteristics of each sub-group in a groupcomprising a plurality of the sub-groups, and the voice over Internetprotocol service class table per call type is prepared based oncharacteristics of each call.
 24. A method, comprising: determining aservice class, comprising of: receiving a voice over Internet protocolcall service request from a subscriber by way of a public branchexchange; determining a voice over Internet protocol service class byreferring to a voice over Internet protocol service class table persubscriber; and determining the voice over Internet protocol serviceclass for the call referring to the voice over Internet protocol serviceclass table per call type when the voice over Internet protocol servicecan be provided in a voice over Internet protocol trunk service levelcorresponding to the voice over Internet protocol service class of thesubscriber; determining whether a voice over Internet protocol servicecan be provided in the service level, comprising of: determining whetherthe voice over Internet protocol service can be provided in the voiceover Internet protocol trunk service level corresponding to the voiceover Internet protocol service class of the subscriber; and determiningwhether the voice over Internet protocol call service can be provided ina voice over Internet protocol trunk service level corresponding to thevoice over Internet protocol service class of the call; and providingthe voice over Internet protocol service, comprising of: looking up anavailable voice over Internet protocol trunk port when the voice overInternet protocol call service can be provided in the voice overInternet protocol trunk service level corresponding to the voice overInternet protocol service class of the call; providing the voice overInternet protocol call service through the available voice over Internetprotocol trunk port; and providing a voice call service through thepublic switched telephone network when the voice over Internet protocolservice cannot be provided in the voice over Internet protocol trunkservice level corresponding to the voice over Internet protocol serviceclass of the call.
 25. The method according to claim 24, wherein thevoice over Internet protocol trunk service level is decided based on anoccupancy rate of a bandwidth out of a total bandwidth, the bandwidthbeing accumulated every time a voice over Internet protocol call serviceis provided.